1. Field of the Invention
The present invention relates generally to hard copy apparatus, more particularly to printing and methods employing rewritable media, and specifically to printing systems adapted for a rewritable media using a coating of a bistable, bi-modal molecular colorant that is electrical field switchable.
2. Description of Related Art
Electrostatically polarized, bichromal particles for displays have been known since the early 1960's. The need for an electronic paper-like print means has recently prompted development of at least two electrochromic picture element (pixel) colorants: (1) a microencapsulated electrophoretic colorant (see e.g., U.S. Pat. No. 6,124,851 (Jacobson) for an ELECTRONIC BOOK WITH MULTIPLE PAGE DISPLAYS, E Ink Corp., assignee), and (2) a field rotatable bichromal colorant sphere (see e.g., U.S. Pat. No. 5,604,027 (Sheridon, assignee Xerox Corp.). Each of these electrochromic colorants is approximately hemispherically bichromal, where one hemisphere of each microcapsule is made the display background color (e.g., white) while the second hemisphere is made the print or image color (e.g., black or dark blue). The colorants are field translated or rotated so the desired hemisphere color faces the observer at each pixel. In commercial practice, these Xerox™ and E Ink™ products rely upon a constant electrical field to maintain an image on a screen or other forms of media employing such technology.
Assignee herein, Hewlett-Packard Company, has gone beyond these microcapsule-based colorant technologies by creating a bi-modal molecular colorant having a variety of uses, including for displays and rewritable media. In some embodiments, the molecules are also bistable, meaning that an electronic holding field is not necessary to maintain a particular state. The term “rewritable” as used herein should be understood to mean writable and erasable. In the main, the goal of such electronic rewritable product development is to provide a means for producing electronic images that truly resembles hard copy in appearance and readability. The Appendix hereto provides a detailed description of one of the Hewlett-Packard™ inventions in this field of technology.
Mobile computers of the “laptop,” “notebook,” and “palmtop” styles and telecommunication devices employing a visual display are typically used during business travel or otherwise away from the office and consequently must be lightweight, fit comfortably within a standard briefcase or handbag, and be battery operated. These same mobile devices have commensurately small, low resolution displays, generally usually liquid crystal technology displays (“LCD”) that are restricted to displaying only a few words or, at best, a few lines, of text. Such displays severely limit the device-human interface; they are difficult to read due to low contrast and narrow-included viewing angle. With the increase in the use of such mobile computer and telecommunication devices, there is a growing, unfilled need for small, mobile, hard copy printing appliances and printers that are integrated into, or adapted for use with, such mobile computer and telecommunication devices.
While state of the art printing is a convenient alternative to reading poorer quality, electronic, visual display information, mobile computer and telecommunication device users typically do not carry, nor want to carry, portable inking printers (e.g., the commercially available HP™ portable DeskJet™ series) and a supply of paper in mobile work situations. Furthermore, what would be printed is generally read once and discarded or kept only for a short working period. Mobile computing and telecommunication applications, therefore, are ideally suited for printing on media that can be reused many times, i.e., a rewritable medium.
Conventional printer technologies are not conducive to the aforementioned needs of mobile appliances. Ink, toner, and thermal-based technologies produce relatively permanent prints, but are typically not briefcase compatible, and require power in excess of adequate, small cell, battery operation.
There is a need for a convenient portable printing apparatus and rewritable media system.